1. Field of the Invention
The present invention relates to an integrated circuit that transfers programs or data used by CPU from external memory to internal memory and particularly decodes encoded sound data.
2. Description of the Related Art
DVD players decode encoded video data and sound data to play back video and sound. FIG. 8 illustrates a sound decoder 100 mounted on these DVD players, which decodes encoded sound data. The sound decoder 100 comprises a DSP (Digital Signal Processor) 101 and embedded memory 102 such as an SRAM and a ROM. The DSP 101 decodes encoded sound data using a program and data stored in the embedded memory 102.
As an encoding method for sound data for DVDs, various standards such as Dolby Digital, DTS, and Linear PCM are available. Programs and data for all these standards may be stored in the embedded memory 102 of the sound decoder 100. In this case, as the number of encoding methods to deal with increases, the necessary capacity of the embedded memory 102 of the sound decoder 100 increases.
Usually, inside an integrated circuit such as the sound decoder 100, a cache memory of small capacity is provided, and outside the integrated circuit, a memory of large capacity is provided. In the process by the integrated circuit, if necessary data exists in the cache memory, the data can be obtained faster compared with obtaining from the external memory. Furthermore, where the cache memory is used, so-called pre-fetch is performed in which to predict programs and data that will become necessary in the integrated circuit in the future and to load the programs and data from the external memory into the cache memory in advance (refer to Japanese Patent Application Laid-Open Publication No. H10-63574).
As described above, a program and data for each encoding method for sound data need to be stored in the embedded memory 102 of the sound decoder 100. Hence, as the capacity of the embedded memory 102 increases, the chip area of the sound decoder 100 becomes larger thus increasing costs.
Moreover, it is possible to store programs and data necessary for encoding sound data in the external memory of the sound decoder 100 and provide a cache memory in the sound decoder 100. However, where the cache memory is used, a cache miss may occur even if pre-fetch with prediction is performed. If a cache miss occurs, the DSP 101 needs to obtain a program and data from the external memory thus reducing the processing speed of decoding. The sound decoder 100 has encoded sound data continuously input thereto. Hence, if processing speed is reduced due to a cache miss, smooth playback cannot be performed.